At trendy East Village-based Molecule Water Café, customers are happily paying $2.50 (£1.59) for a glass of New York City tap water.

So what’s so special about the tap water at this recently-opened establishment?

The secret to Molecule’s success, according to its owners, is a £16,000 filtering machine which uses ultraviolet rays, ozone treatments and reverse osmosis to purify New York’s tap water.

Despite the fact that New York mayor Michael Bloomberg recently claimed the city’s water to be some of the cleanest in the US, those behind Molecule aren’t convinced.

When asked about the quality of New York tap water, Adam Ruhf, co-founder of the café, doesn’t hold back.

‘Terrible,’ he said. ‘I don’t want chemicals in my water. I don’t even want chlorine in my water. Chlorine is like bleach. Do you want to drink bleach? No one wants to drink bleach. So that’s my opinion on New York tap water.’

If the thought of paying for tap water sounds slightly ridiculous, you’ll probably be shocked to learn that some of the biggest bottled water brands have been slapping a price on it for years.

‘Coca-Cola’s Dasani and Pepsi’s Aquafina do essentially the same thing, taking local tap water and treating it further, putting it in a bottle and charging a major price increase to consumers,’ said Professor Steve E Hrudey, environmental toxicology expert at the University of Alberta in Canada.

Mr Ruhf cites the presence of chlorine as the reason for his dislike of tap water but in reality it’s pathogens, not chemicals, which pose the biggest problems.

‘Chemicals aren’t the biggest danger in drinking water,’ said Prof Hrudey.‘Microbial pathogens – bacteria, viruses and protozoa – are the most pervasive and tangible threat to drinking water safety and the failure to treat drinking water properly is the reason that the World Health Organization estimates that more than a million people die every year from waterborne diseases.’

And that’s not just third world countries, either. In 1993, 400,000 people living in and around Milwaukee became ill after drinking water that was contaminated with the pathogen cryptosporidium.

‘The UK has also had outbreaks of this pathogen in Oxfordshire in 1989 and Torbay in 1995,’ said Prof Hrudey, adding that an outbreak in Walkerton in Ontario, Canada in May 2000 killed seven people.

‘So there is ample evidence of the ever-present threat to drinking water safety from microbial pathogens, but the media and bottled water vendors like to focus on chemicals because they sound more dangerous.’

So how do we know if our water is safe? For the most part, we have to trust the authorities, and luckily, today’s state-of-the-art labs, combined with daily testing, help to ensure Britain’s tap water complies with rigorous safety standards and has helped make British tap water some of the safest in the world.

On the other side of the Atlantic, Professor Deborah L Swackhamer, from the Water Resources Center at the University of Minnesota, said the water in New York’s water café was likely to be fine.

‘Since the source water of the Molecule cafe’s water is tap water, it’s probably safe, but many other drinking water sources for bottled water are not necessarily safe.

‘While there are endless regulations and standards when it comes to tap water, bottled water in general isn’t regulated by the government in the same way as tap water – it is considered a beverage, like a soft drink – a consumer food choice and not a right, like the right to safe drinking water.’

According to Professor Edward Bouwer, from John Hopkins University in Baltimore, the popularity of bottled water is largely due to our desire to protect ourselves from the unknown.

‘The source and type of treatment for tap water is largely unknown for the consumer, so this is an involuntary supply,’ he said.

‘Bottled water with a nice label or a certain brand feels like a voluntary choice of what water to drink. We tend to be more comfortable with voluntary choices and more willing to accept a higher risk.’

Unfortunately, the increased popularity of bottled water could mean trouble for our tap water. When we are spending so much on the bottled stuff, are we really willing to fork out extra taxes to improve the quality of what comes out of the tap?

‘The reason why failures occasionally happen is usually because the public undervalues tap water,’ said Prof Hrudey.

‘Often they will, ironically, be reluctant to pay for upgrades to their water utilities to assure competence and the kind of extreme vigilance that is required to assure safe water of high quality is delivered to all customers.’

In the meantime, bottled water will continue to fly off the shelves and in a world where celebrities are regularly paid to be pictured with certain brands, this isn’t a craze that’s set to slow down anytime soon.

‘It’s trendy, a fad, and people will buy anything that is marketed well – whether it makes sense or not,’ said Prof Swackhamer.